Telephone system



A Lil 22 1924.

p I w. L. CASPER TELEPHONE SYSTEM Filed Sent. 22. 1920 //2 ven for [WW/am L Casper 5 I y Afiy Patented Apr. 22, 1924.

UNITED STATES 1,491,334 PAT ENT OFFICE.

WILLIAM LEE CASPER, OF BROOKLYN, NEW YORK, ASSIGNOR TO.WESTERN ELECTRIC COMPANY, mconronn'rnn, on NEW YORK, N. Y.,

A CORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

Application filed September 22, 1920. Serial No. 411,887.

To all whom it may concern:

Be it known that I, WILLIAM Lnn CAsPnR,

a citizen of the United States, residing at Brooklyn, in the county of Kings and State of New York, have invented certain new and useful Improvements in Telephone Systems,

of which the following is a full, clear, concise, and exact description.

This invention relates to telephone systems and more particularly to such systems employing long transmission lines over which both telephonic and signaling currents may be transmitted.

It is frequently the practice to introduce a repeating coil in a long telephone trans-- mission line circuit to inductively join the long external and the relatively short internal or terminating sections of the line. The so-called impedance of the terminating section and the local apparatus associated therewith during conversation usually varies greatly from the impedance of the external section of the line leading from the distant station. Since it has been determined that the best transmission of the voice currents is obtained when the impedances of these sections of the line circuit are approximately equal, it has been customary to design the coils to compensate for these differences in impedances at frequencies within the voice range, thus providing what are known as inequality type repeating coils.

However, the signaling over telephone lines of this character is usually accomplished by means of currents having frequencies outside of the voice range and these inequality type coils, which are designed primarily to transmit the conversational currents, are not particularly well adapted for the etiicient transmission of the signaling currents.

In order to expedite the operation of an exchange, it is desirable to employ the same source of signaling currents for signaling over all of the various lengths and types of line circuits terminating at an exchange. The signaling current generally employed in connection with the local line circuits, which constitute the majority of the lines terminating thereat, has a frequency of approximately 16 cycles per second which is considerably below the frequencies encountered in connection with the transmission of the voice currents.

The object of this invention is to provide an improved signaling means for systems of this character.

In order to attain the object of the present invention, the inductive coupling of the external and terminating sections of a line circuit is arranged to compensate for the differences in the impedances of such sections at the usual low infra voice frequencies em ployed for signaling purposes, as well as for the higher frequencies employed for talking purposes. More specifically the invention consists of the placing of additional windings upon the repeating coil associated with the terminating section of the line so as to provide a coil of proper ratio as far as the low frequency signaling currents are concerned. The signaling responsive de vice is included in a circuit comprising these windings and suitable reactance to present a high impedance circuit to the higher frequencies employed in talking, and to present a very low impedance to the lower frequencies used for signaling purposes. Suitable capacitance is inserted in the talking circuit to present a high impedance to the lower or signaling frequencies and a relatively low impedance to the talking frequencies.

For a more complete understanding of this invention, reference should be had to the followingdescription considered in c0nnection with the accompanying drawing, in which the figure illustrates the invention as applied to a long telephone transmission line circuit of the usual type.

As shown on the drawing, B, connected in any well known manner with an ordinary operators connecting or link circuit A at an ofiice X, extends to an otiice Y. All portions of the line and link circuits unessential to a proper understanding of the invention are omitted. At oifice Y the line circuit B terminates in a repeating-coil 3, comprising windings 4:, associated a line circuit with the external section of the line circuit ing coil 3, are connected to an ordinary terminating jack 12 through condensers 19, while the windings 5 and 7 are connected in series with windings 6 and are included in a circuit in which a suitable electroresponsive device or relay 8 and a condenser 9 are also included. The relay 8 controls a locking relay 10, which, in turn, controls a suitableline signal lamp 11, and is in turn controlled by a sleeve relay 13 associated with the jack 12. For connection with the jack 12 an ordinary operators cord circuit C is provided having a plug 14 and an operators telephone set 15. Only such portions of the cord circuit as are necessary to a proper understanding of the invention are shown.

The windings 4: and 6 of the repeating coil 3 are so designed and possess the proper electrical characteristics to compensate for the difference between the impedance of the external portion of the line circuit B including the operators telephone set 1 at ofiice X, and the impedance of the internal or terminating section of such line circuit 13 including the operators cord circuit C and associated operators telephone set 15. The windings and 7 of the repeating coil 3, when used in cooperation with the windings 6 and 41, provide a repeating coil which is suitable for the efficient transmission of the low frequency signaling currents. Due

to the condensers 19 in the tip and ring conductors, the circuit leading to the jack 12 is tuned for talking frequencies but presents high impedance to ringing currents. The impedance of the current path including windings 5, 6 and 7, the winding of relay 8, and the, condenser 9, is very high as regards the usual voice frequency, but is very low as regards the usual signaling frequency.

It is thought that the invention will be more fully comprehended from a description of the operation of the system shown on the drawings. Assuming that the operator at office X desires to converse with the operator at office Y and that suitable connection has been made by means of a plug and a jack or in any other well known manner, between the operators link circuit A. and the line circuit B, the operator actuates the ringing key 2. Ringing current of the usual low frequency employed in signaling over short or local lines, is thereby impressed upon the external section of the line circuit B, including the windings & of the repeating coil 3 and is induced by means of the windings 5, 6 and 7, into the circuit including the winding of relay 8 and the condenser 9. The current thus transmitted over the external portion of the line circuit, being of the frequency for which the circuit including the relay 8 is resonant, such relay responds, and, closing its contact, causes the operation of relay 10 over an obvious circuit. Relay 10, in operating, causes the illumination of the line lamp 11 over a self evident circuit and completes an obvious locking circuit under the control of the sleeve relay 13.

The operator at otfice Y, observing the illumination of lamp 11, inserts the plug 14 of cord circuit G into the jack 12, thereby causing the operation of relay 13 over a circuit traceable from battery through the normal local contact of listening key 16, the sleeve contacts of plug 1& and jack 12 and the winding of relay 13 to ground. Relay 10 thereupon releases to extinguish the line lamp 11. Upon the actuation of the listening key 16, operators set 15 is connected to the cord circuit C, and relay 13 is released. Upon the actuation of the listening key 17, to connect the operators set 1 to the cord circuit A, the operators at the offices X and Y may converse over the line circuit B, the voice currents being transmitted by means of the windings 4: and 6 of the repeating coil 3. These latter windings are so designed as to transmit most efliciently the voice currents and the circuit including the relay 8 is of B such high impedance to these currents, that no material eflect upon their transmission is produced by such circuit. Upon the completion of the conversation the operator at office Y removes the plug 1& from the jack 12 and upon the restoration of the listening keys 16 and 17 all apparatus is restored to normal.

It is thus evident that in accordance with the present invention a means is provided in a long transmission line circuit which will not only efiiciently transmit the ordinary talking currents, but will also efficiently transmit the lower frequency currents usually employed for signaling purposes, thus permitting the use of thesame source of signaling currents as is employed in connection with the local line circuits.

What is claimed is:

1. In a telephone system, in combination, two sections of line circuits of different impedances for transmission of talking and signaling currents, and an inductive coupling element between said line sections having different ratios of transformation for voice range frequencies and for infra voice range frequencies.

2. In a telephone system in combination, a transmission line having an external and a terminating section, a repeating coil having primary and secondary windings inductively coupling said sections, said primary and said secondary windings effectively transmitting currents within the voice range of frequencies, and additional secondary windings for the repeating coil for cooperation with the primary and first-mentioned secondary windings for efficiently transmitting currents of low frequency.

3. In a telephone exchange system, a transmission line circuit interconnecting two offices, external and internal sections therefor, a telephone set at each ofiice, means for connecting such telephone sets with the transmission line circuit for conversation, a

source of signaling current at one office, switching means for connecting such source with the line circuit, a repeating coil at the other ofiice, a winding thereof included in each section of the line, said windings cooperating to transmit the talking current, a responsive device at the other office, and additional windings for said coil cooperating with the other windings to transmit the signaling current to said responsive device.

4. In a telephone exchange system, a transmission line circuit, sources of voice and infra voice frequency currents at one end thereof, means for selectively associating said sources with the line, a repeating coil associated with the line, primary and secondary windings thereof cooperating for the transmission of voice frequencies, additional secondary windings of the repeating coil cooperating therewith for the transmission of infra voice frequency currents, a circuit associated with the additional windings resonant to the infra voice frequency currents, and means included in the circuit responsive to the infra voice frequency currents.

5. In a telephone system, two line sections of different impedances for the transmission of currents of different ranges of frequencies, and an inductive coupling element between said line sections havin different ratios of transformation for ifferent frequency ranges.

6. In combination, a line, a transformer having a winding in said line, a second winding inductively coupled to said first winding, a circuit connected to such points of said second winding that the impedance across the terminals of said first winding looking in the direction of said circuit is approximately the same as the impedance looking in the opposite direction for a particular frequency, and a second circuit connected to such other points of said second winding that theimpedance across the terminals of said first winding looking in the direction. of said second circuit is approximately the same as the impedance looking in the opposite direction for a different frequency.

7. In combination, a line, a transformer having a winding in said line, a second winding inductively coupled to said first winding, a circuit connected to such points of said second winding that the impedance across the terminals of said first winding is approximately equal to the impedance looking in the opposite direction for a particular frequency, a second circuit connected to such other points of said second winding that the impedance across the terminals of said first winding looking in the direction of said circuit is approximately the same as the impedance looking in the opposite direction for a different frequency, and means included in one of said circuits non-responsive to that frequency for which the other circuit has the proper impedance.

8. In combination, a line, a transformer having a winding in said line, a second winding inductively coupled to said first winding, a circuit connected to such points of said second winding that the impedance across the terminals of said first winding is approximately equal to the impedance looking in the opposite direction for a particular frequency, a second circuit connected to such other points of said second winding that the impedance across the terminals of said first winding looking in the direction of said circuit is approximately the same as the impedance looking in the opposite direction for a diiferent frequency, and means in one of said circuits for preventing the passage of currents of that frequency for which the other circuit has the proper impedance.

9. An electric system comprising a line, a transformer winding connected thereto, a second transformer winding inductively coupled to said first winding, connections for utilizing a portion of said second winding in the reception of certain frequencies from said line, and connections for utilizing said portion and an additional portion of said second winding for the reception of another frequency.

In witness whereof I hereunto subscribe my name this 16th day of September A. D.,

WILLIAM LEE CASPER. 

